(1) Field of the Invention
The present invention relates to a heat treatment furnace. More specifically, the invention is intended to provide a heat treatment furnace for a treatment performed by keeping metal at a high temperature for a certain period and then cooling rapidly the same, which achieves a reduction of running cost and an increase in cooling speed.
(2) Description of Related Art
For example, Ni(nickel)-based superalloy makes full use of its strength when it has a coherent structure in which γ (gamma: alloy matrix) and γ′ (gamma prime; Ni3Al) are in a coherent array. In order to obtain the coherent structure of the γ/γ′ which provides a maximum strength, a heat treatment method of increasing the temperature of the alloy to a temperature closest to a fusing temperature (on the order of 1350° C.), and keeping it for a certain period (on the order of 40 hours) for homogenization, and then cooling the alloy rapidly is required. In this case, the quicker the cooling speed, the better the high precision of the coherent structure formed at the high temperature is maintained, and the higher alloy strength is demonstrated.
Thus, conventionally, a gas fan cooling furnace has been used as means for heating the alloy to a high temperature and then cooling rapidly the same. An example of configuration will be described with reference to FIG. 10. Here, FIG. 10 is a front view schematically showing the configuration in the related art partly in cross section.
In FIG. 10, a heating chamber 100 is formed into a sealed cylindrical barrier shape, and includes a plurality of rod shaped resistance heating elements 111 in the interior thereof in a cylindrical fence pattern. Examples of the material used for the resistance heating elements 111 includes W (tungsten) and Mo (molybdenum).
Cylindrical heat insulating panels 121 to 123 having different diameters respectively are disposed triply so as to surround the plurality of resistance heating elements 111, and a disk-shaped heat insulating panels 131 to 133 are disposed so as to cover upper and lower openings of the heat insulating panels 121 to 123. The W or Mo is also used as a material for the heat insulating panels 121 to 123 and 131 to 133.
When heating the alloy to a temperature close to the fusing point using the heat treat furnace having such a configuration, an alloyA to be heat-treated is arranged at a center portion of a space surrounded by the plurality of resistance heating elements 111 and then air in the interior of the heating chamber 100 is evacuated. Then, when an electric current is fed to the respective resistance heating elements 111, the respective resistance heating elements 111 generate Joule heat, heat up the alloyA to be heat-treated to a temperature close to the fusing point using radiant heat as a heat source, and keep this state for a certain period.
When the certain period has elapsed, electricity having been distributed to the respective resistance heating elements 111 is stopped, high-purity He (helium) gas or Ar (Argon) gas is supplied into the heating chamber 100 as cooling gas via a gas inlet port, not shown, and is blown onto the alloyA to be heat-treated to cool the same. When the heating chamber 100 is filled with the supplied cooling gas, a fan (not shown) is driven to forcedly stir the cooling gas.
In this manner, in the related art, the W or Mo is used as the material of the resistance heating elements 111 and the heat insulating panels 121 to 123 and 131 to 133, and heating of the alloyA to be heat-treated and cooling of the heated alloyA to be heat-treated are performed in the identical space.    Patent Document 1-JP A 7 218144